The present invention relates to an information recording method and information recording/reproducing system utilizing light, heat or magnetization, and more particularly to an optical disk apparatus in which control effective for recording/reproduction is adopted.
An optical change caused by the presence/absence of information recorded portions is detected (see Philips Technical Review, Vol. 40, 1982, No. 6, pp. 157-164), and a beam on one track is scanned once in the track direction so that the recording/reproduction of information is made in the form of a binary signal. As means for providing an improved recording with a high density are known (1) a method, as disclosed by JP-A-3-278320, in which the recording is made with the track pitch of information recording and the pit pitch of information portions being narrowed and (2) a many-valued recording method in which one information is represented by a plurality of pits. As the many-valued recording method, JP-A-3-292631 has disclosed a method in which three-valued digitization is made by homologically changing the size of a pit and JP-A-2-172039 has disclosed a method in which many-valued digitization is made by letting the arrangement of the same pit (or the presence/absence of a pit) have information.
Also, there is a problem that when the writing and erasion of data having the same content are repeated, the same location of a medium is repeatedly irradiated with a laser beam and hence that portion of the medium is deteriorated, thereby resulting in the deterioration of the sensitivity of reproduction. In order to solve this problem, JP-A-3-150725 has proposed a method in which the time of a write data signal is adjusted to shift the writing position of data, thereby suppressing the deterioration of an information recording medium.
Further, JP-A-62-80865 has proposed an optical disk apparatus in which both an MCAV (Modulate Constant Angular Velocity) system and a CAV (Constant Angular Velocity) system can be handled by providing means for changing the frequency of a reference clock signal in accordance with a track position. The MCAV system is a system in which the timing of recording/reproduction is changed in accordance with a track position, and the CAV system is a system in which the recording/reproduction is made with the rotation velocity of a disk being kept constant. Nikkei Byte, 1992, No. 1, pp. 120-133 has disclosed other systems including a CLV (Constant Linear Velocity) system in which the recording/reproduction is made with a linear velocity being kept constant.
As has been mentioned, a technique of making the recording at spatially closed intervals, which is one of high-density recording methods, has a limitation. Therefore, the many-valued recording method has been proposed in which the recording density in the same space is improved. However, the proposed many-valued recording method involves a problem that if a recording or irradiation power is not further enhanced, further many-valued digitization cannot be expected but the higher irradiation power causes a change in form of a recording portion and the thermal deterioration of a substrate. On the other hand, the many-valued recording method in which one information is represented by a plurality of pits having the same form, is the same as the concept in which the size of a pit is made small to provide a spatially closed interval. In order to arrange pits of the same form with a high efficiency, it is necessary to always move the scanning position of a beam in a track width direction with an irradiation start point and an irradiation time being kept constant.
Also, the JP-A-3-150725 proposing the method of performing the writing with the data writing position being shifted in order to prevent the deterioration of the recording medium does not disclose the manner of reproduction. If a reference clock signal is generated on the basis of reference positions (or servo marks) preformatted on a medium and the recording/reproduction is made in synchronism with the generated reference clock signal, as in an information recording medium based on a sample servo format, there is a problem that the shifted recording of data makes it impossible to reproduce the data since a reproduced signal is not synchronous with the reference clock signal.
Further, in the case were the recording/reproduction is made on the basis of the CAV system, there is employed a sample servo system in which a recording capacity is small but the construction of an optical system is simple, thereby making it possible to reduce the size of the apparatus. In the sample servo system, it is possible to detect data, a focusing error and a tracking error by detecting servo marks radially preformatted on an optical disk and time-dividing the servo marks.
However, in the MCAV system or the like, the frequency of a reference clock signal must be changed for each zone or track. Therefore, in the case where the sample servo system is employed in the MCAV system or the like, there is a fear that when access from one zone to the adjacent or next zone is made, it becomes impossible to detect servo marks at a predetermined timing. If the detection of the servo marks becomes impossible in the sample servo system, there is a problem that it becomes impossible not only to make the recording/reproduction but also to have a light beam follow the track.